learn-c

Reference

1. https://www.geeksforgeeks.org/c-programming-language/
2. C in a Nutshell
3. C Primer Plus
4. C Programming Cookbook
5. Century C
6. Data Structures Using C
7. Exterme C
8. Modern C (Next)
9. Modern C for Absolute Beginners

Comment

#if 0
	...
#endif

Wide characters

#include <stddef.h>

wchar_t wc = '\x3b1';

Not all compilers support universal character names

Digraphs and Trigraphs

int arr<::>=<%10,20,30%>;
printf("The second array element is <%d>.\n", arr<:1:>);

int arr[]={10,20,30};
printf("The second array element is <%d>.\n", arr[1]);

Digraph	Equivalent
<:	[
:>	]
<%	{
%>	}
%:	#
%:%:	##
or trigraphs Ex: ??( -> [

printf("Cancel???(y/n) ");

printf("Cancel?[y/n) ");

printf("Cancel\?\?\?(y/n) "); // Cancel???(y/n) 

Enum

enum {OFF, ON, STOP=0, GO=1, CLOSED=0, OPEN=1};

// Auto size
typedef enum A { OFF, ON }; // sizeof A; 4
typedef enum B { OFF, ON = 0xFFFFFFFFFFFFFFFF }; // sizeof B; 8

The Alignment of Objects

// C11
_Alignas(4) short a; // sizeof a; 2 and _Alignof(a); 4
// #include <stdalign.h> _Alignas -> alignas and _Alignof alignof

Literals

Suffix	Type
0	int
0U	unsigned int
0L	long
0UL	unsigned long
0LL	long long
0llu	unsigned long long
0.0	double
0.0f	float
0.0L	long double

Literals	Type
85	decimal
0213	octal
0x4b	hexadecimal

// Float [+/-] <Mantissa> <e/E> [+/-] <Exponent>
double a = 67e-12; // 64.0*10^-12

Prefix	Examples	Type
none	'a', '\t'	int
L	L'a', L'\u0100'	wchar_t (stddef.h)
u	u'a', u'x3b3'	char16_t (uchar.h)
U	U'a', U'\u24FA'	char32_t (uchar.h)

Escape sequences: \o[oct], \x[hex], \u or \U universal character Wide-string literal is defined using the prefix L: L"Hello"

// Multiple line
char* str1 = "xin \
chao";

char* str2 = 
"string1\n"
"string2";

char* str3 = R"(
	string1
	string2
)";

Generic Selections C11

// _Generic (expression, generic association 1 [, generic association 2, ...])
#define get_type(expr)    \
	_Generic((expr),      \
	       int : "int",   \
	      char : "char",  \
	    double : "double" \
	)

#define cbrt(X)              \
	_Generic((X),            \
	    long double : cbrtl, \
	        default : cbrt,  \
	          float : cbrtf  \
	)(X)

Pointer arithmetic

doubled dArr[5]={0.0,1.1,2.2,3.3,4.4}, *dPtr = dArr;
dPtr = dPtr + 2;
int i = dPtr - dArr; // 2, the index of the array element that dPtr pointer to.
// The type of i: ptrdiff_t (stddef.h)

Array

int a[] = { [1000] = -1 }; // Create an array of 1001 elements

Flexible Structure

typedef struct { int len; float array[]; } DynArray_t;
// sizeof DynArray_t = 4
DynArray_t * daPtr = malloc(sizeof(DynArray_t) + 10*sizeof(float));
// This initialization reserves space for 10 elements

Anonymous structure

union WordByte
{
	short w;
	struct { char b1, b1 }; // Anonymous structure
};
union WordByte wb = {256};
char lowByte = wb.b0;

_Static_assert

// Only an instruction to the compiler to test an assertion.
_Static_assert(sizeof(int)>2, "16-bit code not supported");
// static_assert (assert.h)

Storage Classes

Storage Speciflier	Storage	Initial value	Scope	Life
auto	stack	Garbage	Within block	End of block
extern	Data segment	Zero	global Multiple files	Till end of program
static	Data segment	Zero	Within block	Till end of program
register	CPU Register	Garbage	Within block	End of block

int x; // Zero
void foo()
{
	static int y; // Zero
	int z; // Garbage
}

F() and F(void)

void func1() {}
void func2(void) {}

void main()
{
	fun1(10, "abc", -1.0f); // Compile and runs fine
	fun2(10, "abc", -1.0f); // Fails in compilation
}

Executed before and after main

// With GCC family of C compilers
void myStartupFun (void) __attribute__ ((constructor)); // executed before main()
void myCleanupFun (void) __attribute__ ((destructor)); // executed after main()